Conventional toilet tanks have a lever mounted on the outside of the tank which is pushed down in order to flush the toilet. A chain is thereby caused to open a flapper valve at the bottom of the tank. Opening this valve allows the water in the tank to exit the tank and flow into the toilet bowl, thus flushing the toilet bowl. As the water level in the tank drops, a large float pivotally mounted on a ballcock at the top of the tank descends with the water level, thus causing the ballcock to open. Typically, the ballcock opens when the tank is still two-thirds full and is still emptying. The opening of the ball cock permits the inflow of more water, which begins to flow into the tank at the same time that water is flowing out the bottom of the tank through the flapper valve, which is quite wasteful.
Various attempts have been made to reduce the amount of water used in each flush, for economic and water conservation reasons. One simple way is to adjust the vertical position of the large float to a lower level so that is causes the ballcock to shut off at a lower water level. Accordingly, less water is held in the tank for use when flushing. This adjustment is often done simply by bending the metal arm that the large float is mounted on. While this method does reduce the amount of water being used, it does not stop water from flowing into the tank through the ballcock while water is simultaneously flowing out of the tank through the flapper valve.
Other methods such as putting bricks in the toilet tank have also been used to reduce the amount of water used during flushing of the toilet. Again, this method does not stop water from flowing into the tank through the ballcock while water is simultaneously flowing out of the tank through the flapper valve.